Many integrated circuits use a main memory, such as an electrically erasable programmable read-only memory (EEPROM), to store data persistently. However, memories such as EEPROMs may only be read a certain number of times before the data stored within those memories is lost. Because of this, a shadow memory, such as a random access memory (RAM), is sometimes used to store a copy of the data in the main memory. The shadow memory may then be read instead of the main memory, reducing the number of reads for the main memory and allowing the main memory to last longer.
Disadvantages associated with the use of a typical shadow memory include the fact that glitches on the supply line or other analog signals may cause the shadow memory to become corrupted. To overcome this difficulty, typical systems provide a complex under-voltage detection circuit that may be used to detect conditions that might corrupt the shadow memory. If these conditions are detected, the main memory is copied into the shadow memory again.
However, because of the complexity of the under-voltage detection circuit, this approach requires the use of a substantial amount of chip space. In addition, only corruption due to under-voltage conditions is detected. Thus, corruption resulting from other sources goes undetected with this approach.
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